This invention relates to a process for fire resistant cellulosic materials and rendering cellulosic materials leach resistant. More particularly, the invention relates to a process of using aluminum phosphate to make wood fire resistant and render such wood leach resistant. This invention relates also to a composition comprising cellulosic materials and aluminum phosphate which is fire resistant.
Wood, a natural cellulose material, is used in home construction in roofing, frames, support and plywood; however, wood has use restrictions in roofing as there is no approved commercial fire resistant treatment. If homes were not protected with nonflammable roofs, a fire could easily jump from house roof to house roof, especially with high winds.
Effective fire resistant treatment of wood for both exterior and interior uses under conditions of leaching and weathering is needed because desirable properties of wood must be preserved after initial fire resistant treatment.
Fire retardants are added or applied to a cellulosic materials such as wood products to increase the resistance of that cellulosic material to fire. Such materials are less flammable than the cellulosic (wood) they protect. Some fire retardants prevent the spread of flame; others burn and thereby create a layer of char that inhibits further combustion. At the same time, some organic fire retardants may produce fairly toxic gases during exposure of the treated material to fire temperatures which may present problems for persons caught inside a burning building and for fire fighters.
The chemicals in a fire resistant composition determine how it works. Most flame retardants contain elements from any of three groups in the Periodic Table of Elements (Group IIIa (including boron and aluminum), Group Va (including nitrogen, phosphorus, arsenic, and antimony), and Group VIIa (including fluorine, chlorine, and bromine). Aluminum (sometimes as aluminum oxide) increase the amount of char formed in the early stages of a fire. This char forms a protective layer that prevents oxygen from reaching the inner layers of the protected material and thus sustaining the fire.
Phosphorus is a flame retardant in its solid and liquid phases which works by forming a surface layer of protective char on wood. Compounds of phosphoric acid are most frequently used as flame retardants for the first class of materials. On heating, sometimes phosphoric acid reacts with the cellulose to produce large amounts of carbon char and incombustible gases, such as steam and carbon dioxide, which either prevent fire from starting or smother it.
Various U.S. Patents disclose concepts for reportedly rendering wood flame proof. These patents include U.S. Pat. No. 4,981,518 issued to Melvin H. Sachs on Jan. 1, 1991 which discloses a cellulose filler material, such as wood chips, which are rendered nonflammable by encapsulation within a binder which is formed in an exothermic reaction from mixing a powdered base metal oxide and a weak acid, such as aluminum phosphate, which may be in the form of an acidic solution. This patent further discloses a method of making the bonded composite structure including the steps of mixing the weak acid and powdered base metal oxide, encapsulating the fibrous cellulose material within the binder and rendering the fibrous cellulose material nonflammable, thereby forming the slurry mixture into a predetermined form and setting the formed mixture into a solid.
U.S. Pat. No. 4,857,365 which issued to Shozo Hirao et al. on Aug. 15, 1989 and U.S. Pat. No. 4,731,265 which issued to Shozo Hirao et al. on Mar. 15, 1988 disclose a modified wood which is reportedly produced by reacting two water-soluble solutions, one with cations (selected from a group containing aluminum) and one with anions (from a group containing phosphoric acid) which react to form an insoluble, nonflammable, inorganic compound. A method of manufacturing a modified wood material is disclosed in these patents which reportedly can position within a raw wood material, an insoluble, nonflammable, inorganic compound using a highly efficient reaction achieved between cations and anions by sequentially immersing the raw wood material at least three times alternately in each of, and different one from that employed immediately before of a first water-soluble, inorganic substance solution containing cations and a second water-soluble, inorganic substance solution containing anions.
JP 63159008 discloses modified wood which is impregnated with insoluble, incombustible material using two aqueous solutions. A physical stimulus, which may be microwave heating, is given to the wood to promote formation of the insoluble material. Ions with a (3+) charge may be in one solution and phosphate ions in the other.
JP 48046195 discloses that pulp and wood are fireproofed with aluminum phosphate and silicates.
Aluminum phosphate has been manufactured in the United States since the late 1940s. While there is prior art as to compositions for fireproofing wood, including some compositions containing aluminum and some compositions containing phosphorus, a more efficient process and composition for fire resistant wood and rendering it leach resistant is provided herein using aluminum phosphate.
It an object of the invention to provide a treated cellulosic material which has improved fire-resistant and leach-resistant properties.
It is a further object of the invention to provide a process for preparing a wood shingle and plywood compositions having improved fire-resistant and leach-resistant properties.
It is another object of this invention to provide an aluminum iron phosphate composition which renders wood fire resistant and leach resistant.
The above and other objects are achieved in this invention more particularly described in the specification hereinafter following.
This invention comprises a process for contacting a cellulosic (wood) product with an aqueous solution of aluminum phosphate wherein the molar ratio of Al:P ranges from less than 1:1, optionally containing a metal oxide component, which is followed by removal of water (such as by evaporation) from the cellulosic (wood) product and subsequent curing of the dried cellulosic (wood) product to produce a treated cellulosic product. The cellulosic treated (wood) product is thereby rendered flame proof. (As employed herein, the abbreviation xe2x80x9cAlxe2x80x9d means aluminum and xe2x80x9cPxe2x80x9d means phosphorous.)
This invention further comprises a cellulosic material on which is deposited aluminum phosphate and (optionally a metal phosphate) which has been cured to form a condensed phosphate and wherein the chain length (n) ranges from about 10 to about 10,000.
This invention comprises a process for preparing a fire-resistant cellulosic material which comprises contacting cellulosic material with an aqueous solution of aluminum phosphate wherein the molar ratio of aluminum to phosphorous is less than 1:1, to about 0.02-0.7 to 1, and more preferably from 0.3-0.4 to 1, optionally containing a metal oxide such as ferric/ferrous oxide, to form an initially treated cellulosic material comprising aluminum phosphate and optionally iron phosphate and an increased amount of water, and removing excess water from and curing said initially treated cellulosic material to form a fire-resistant cellulosic material. The cellulosic material is preferably wood and the wood is preferably a shingle or plywood. In practicing the process of this invention, preferably a single solution is employed which comprises aluminum phosphate, although separate solutions containing aluminum ions and another solution containing phosphate ions could be employed if desired. This invention also comprises a cellulosic material on which is deposited aluminum phosphate and (optionally a metal phosphate) which has been cured to form a condensed phosphate and wherein the chain length (n) ranges from about 10 to about 10,000. The term xe2x80x9cdepositedxe2x80x9d includes deposited, in contact with, on, in, within and the like.
A metal oxide is generally employed in this process and typically the aluminum phosphate/metal phosphate aqueous composition is deposited on or impregnated in a cellulosic material such as wood by contact, ultrasound, vacuum/pressure or heat treatment. This impregnation is followed by evaporation of the water at the boiling temperature of the phosphorous solution, and then curing by heating the treated cellulosic material to provide the treated cellulosic material product.
As employed herein, the term xe2x80x9ccellulosexe2x80x9d includes the complex carbohydrate (C6H10O5)m that is composed of glucose units and which forms the main constituent of the cell wall in most plants, including woody plants such as trees, and includes those cellulosic materials on which one can cure the phosphate compositions used in this invention. As employed here, the term xe2x80x9cwoodxe2x80x9d includes without limitation softwood and hardwood and products made in part or whole from wood or a part thereof, including plywood and oriented strand board, shingles and shakes, and paper and paper products which are especially preferred cellulosic materials useful in this invention and includes those wood materials on which one can cure the phosphate compositions used in this invention.
Further as employed herein, the term xe2x80x9cfire-resistantxe2x80x9d means highly resistant to fire such as when cellulosic material is exposed to a flame.
Also as employed herein, the term xe2x80x9cleach resistantxe2x80x9d means having the capability to retain aluminum phosphate after subsequent contacting with water.
More particularly, this invention is carried out in a process whereby wood (as a preferred cellulosic material) is preferably soaked in an aqueous solution of aluminum phosphate with an Al2O3xe2x80x94P2O5 molar ratio preferably of about 0.33+/xe2x88x920.1 in an initial process step.
The aluminum phosphate solution is maintained at or heated to a temperature from about 60xc2x0 C. to about 100xc2x0 C., preferably from about 80xc2x0 C. to 90xc2x0 C., by the addition of a suitable amount of heat as necessary using a suitable, convenient method of heating. The wood to be treated is added to the aluminum phosphate solution or the aluminum phosphate solution is added to the wood. The heating to effect curing of the aluminum phosphate may be carried out by a conventional means known to those of skill in the art after reading this specification.
The concentration of aluminum phosphate in the solution is generally from about 0.5% by weight to about 45% by weight solids of the total solution and preferably from about 5% by weight to about 20% by weight although greater or lesser concentrations may be employed if desired.
The number of repeating units of aluminum condensed phosphate formed as a result of curing is conveniently herein designated as (n), wherein n is an integer varying from about 20 to about 100 or more, wherein the molar ratio of Al:P is less than 1:1, preferably from 0.2 to 0.7 to 1, and most preferably from 0.3 to 0.4 to 1. Aluminum phosphate solutions are described in 1 and 2 J. R. VAN WASER, PHOSPHORUS AND ITS COMPOUNDS (Interscience Publishers, 1961), which is incorporated herein by reference in its entirety.
The elapsed time during which the wood is contacted with aluminum phosphate solution depends to a large extent on the size of the wood to be treated but illustratively with the sizes of wood employed in the Examples of this invention the contact time is from about 5 minutes to about 300 minutes and more preferably from about 15 minutes to about 60 minutes or so. Those of skill in the art will recognize that greater or lesser amounts of contact time may be employed and that the time of contacting will vary with the type of wood and the size of the piece of wood employed. Those of skill in the art will recognize that the amount of time preferred is that time which will afford sufficient and effective contact time of the wood with the aqueous solution containing the aluminum phosphate. Generally, the amount of contact time preferred is that time needed xe2x80x9cto soakxe2x80x9d the wood in the aluminum phosphate solution. Preferably the contact time of the wood and the phosphate solution is such that a single contact of wood and phosphate solution using the particular method of contacting is sufficient.
The wood is preferably placed within the phosphate solution so as to afford the maximum amount of wood and phosphate in contact with one another. The wood may be dipped in the phosphate solution one or more times or may be allowed to remain in the phosphate solution and soak but a single contact or dip is preferred. Any convenient method of contacting the wood and the phosphate solution may be employed, including without limitation, applying a vacuum to the wood, applying pressure to the solution in contact with the wood, dipping, soaking, brushing by brush or by using vacuum, using pressure, air brushing, spraying, splashing, pouring the aluminum solution over wood and the like, although soaking is the preferred method. Even and thorough contacting of the aluminum phosphate solution with the wood is desired for a uniform fire-resistant and leach-resistant product of this invention. The wood may remain in a stationary position while it is in contact with the phosphate solution or the wood may be moved during such contact. A single contact of the wood with the aluminum phosphate solution is sufficient providing that the contact is thorough, uniform and the time is sufficient for the contact to have occurred.
Typically, the wood to be treated is debarked and has an unfinished surface wood allowing for the phosphate solution to be taken up by the wood so that a relatively high uptake of aluminum phosphate will be accomplished. A vacuum pretreatment of the wood is preferred.
The wood is removed from the phosphate solution with which it has been in contact after a sufficient contact time and is allowed to air dry until the surface of the wood seems substantially dry to the human touch, perhaps for a time of about one hour or more or less. This initially treated wood may be placed in a vacuum oven to begin curing so that the temperature therein is in the range from about 30xc2x0 C. to about 80xc2x0 C. or so although greater or lesser temperatures may be employed if desired. This provides dried wood which is preferably uncharged and not burned.
The dried wood being treated can also be placed in a microwave oven and irradiated for about 20 to 40 seconds or so, preferably on full power, to remove more of the initial water without burning or charring the wood being cured. Those of skill in the art will recognize that the purpose of using the microwave energy from the microwave oven is to impart energy to the wood so that a major portion of water is evaporated therefrom and to be able to apply heat to the wood without charring or burning it. However, any convenient means of removing water may be employed as those of skill in the art will readily recognize and use of a microwave oven or equivalent to supply energy for water removal is also convenient.
Typically, the full power or wattage of a preferred microwave oven is about 900 watts, although greater or lesser wattages may be employed as for larger or smaller amounts of wood being heated. The curing time may be about 40 seconds or so and this heat cycle may be repeated three-four times or so when treating shingles of about 10 cmxc3x9710 cm. dimensions. Those of skill in the art will recognize that different brands and types of microwave ovens will have different levels of high wattages and therefore the curing time and curing cycle may vary. In all instances, a sufficient curing time and sufficient cycle is employed.
The time to remove the water is that elapsed time which will be needed as a result of selecting an effective method of water removal and the rate of application of heat or alternative energy means. A sufficient time is employed for water removal and curing. Preferably, the water is removed from the initially treated wood before curing, although such is not required.
This invention is an effective exterior-type fire-resistant and leach-resistant treatment which can be made to red cedar shingles using aluminum-iron phosphate. The process of this invention may also be used for other exterior and interior cellulosic materials.
Typical metal oxide components which may be employed in practicing this invention include ferric/ferrous oxide, ferric oxide, cupric oxide, and zinc oxide (1.23% of a mixture of 3 parts of zinc oxide, 1 part of titanium dioxide and 0.33 parts of silica), mixtures thereof and the like. Ferric/ferrous oxide is the preferred metal oxide component of this invention. Aluminum phosphate is the preferred phosphate with n about 20 (n is the integer representing chain lengths of condensed phosphate).
Those of the skill in the art will recognize that other components may be present in the aluminum phosphate solutions including urea, melamine, dicyandiamide, boric acid, mixtures thereof and the like.
In practicing this invention, it is preferred to produce after drying and curing a composition comprising aluminum condensed phosphate wherein n is about 100 and the metal oxide component is ferric/ferrous oxide.
In a preferred mode, an aluminum-iron phosphate may be deposited on wood by a vacuum/pressure impregnating procedure under overall positive pressure, particularly under pressure from about 5 lbs. to about 35 lbs. per square inch for a period of time from about 0.5 hour to about 1.0 hour to impregnate the wood with aluminum phosphate followed by evaporation of water, acting as solvent for the phosphate, and then curing the treated wood in a microwave oven.
The range for suitable vacuums useful in practicing this invention is from about 0.1 mm Hg to about 50 mm Hg and more preferably from about 5 mm Hg to about 20 mm Hg, although greater or lesser vacuums may be employed as desired.
The range for pressures useful in practicing this invention is from about 5 psig to about 35 psig and more preferably from about 10 psig to about 30 psig, although greater or less pressures may be employed if desired.
After treatment with the process of this invention, the wood may be finished in any desired manner such as by applying paint or another finishing substance or left unfinished.
Without being bound by theory, it is believed that the curing process herein polymerizes water soluble aluminum phosphate or aluminum iron phosphate into a water insoluble aluminum condensed phosphate or aluminum iron condensed phosphate which remains on or in the treated cellulosic ( wood) product. This process releases water of composition. Further, without being bound by theory, it is believed that the practice of this process results in a cellulosic material on which is deposited aluminum phosphate and (optionally a metal phosphate) which has been cured to form a condensed phosphate and wherein the chain length (n) ranges from about 10 to about 10,000. An additional metal condensed phosphate may also be deposited on the cellulosic material as a result of employing an optional metal phosphate in the process of this invention.